This invention relates to the field of transmission of binary encoded digital data, and more particularly to a simplex, point-to-point data link for transmitting such data in a highly reliable manner in an extremely hostile electromagnetic interference environment.
Transmission of digital data between components or electronic subsystems, e.g., avionics systems on high performance military aircraft has been subject to electromagnetic interference even when transmission is by a shielded twisted wire pair. Improvements in reliability have been achieved, notably by a closed loop binary digital communication system as described in copending patent application Ser. No. 614,196, filed May 25, 1984, and assigned to the assignee hereof, which system comprises master and slave transmit/receive units and is capable of operation in a baseband mode. The present invention is particularly well suited for, but not limited to, use as the binary digital data link portion of that system. In such use two of the simplex data links of this invention are combined to form a half duplex communication channel.
All data link design requirements can be grouped into three basic areas of consideration. First, central to every application is the data rate requirement. The upper limit defines the maximum rate of information transfer required by the equipment. Data links are normally categorized as low, medium, or high data rate channels. The circuit design approaches required to optimally implement each type are in most cases significantly different. Secondly, the quality of data transfer is specified. This normally involves some minimum bit error rate (BER) both for the clear channel and in the presence of a specified level of interference. Certain applications can tolerate a relatively large number of transmission errors, while others require virtually error free communication. The circuit design apporaches required for the two link types are different and often very specialized.
Finally, the physical environment the data link must operate in and conform to is specified. For the case of aircraft applications such factors as cable type, cable length, number of interconnects, connector types, shielding and grounding configurations, available power, and maximum transmitter/receiver size and weight are usually determined prior to the data link design. In addition, environmental requirements such as operating temperature range and EMI limits are specified. All of these factors must also be considered in data link design.